This invention relates generally to integrated circuit (IC) packages, and more particularly to a device and method for attachment of a heat sink to such a package. Heat sinks made of thermally conductive metal are widely used with electrical circuit components. Even though small components do not generate much heat, they are not able to endure much heat. If they are integrated circuit devices, their performance may deteriorate at higher temperatures. Their useful life may be shortened too. Therefore, heat sinks are often used with integrated circuit packages. Spring clips have been used to attach the heat sink to the package. Usually there is some interface material between the package and the heat sink. While it may serve the purpose of electrical isolation, its primary purpose is to transfer the heat from the IC package to the heat sink. An optimum combination of dielectric strength and thermal conductivity is not always available. In any case it is desirable to have good conformance of the interface material with both the package and the heat sink to have good thermal transfer. To provide good conformance, adequate contact pressure is necessary. With some package, interface and heat sink materials, the contact pressure needed and obtainable by the spring clips is more than the package can withstand without damage. In such instances, adhesives have been used in lieu of clips to secure the heat sink to the package.
One conventional way to provide the interface between the IC package and the heat sink is to apply a thermally conductive grease or paste to the package substrate and to the heat sink. This requires some skill in neatly applying the grease or paste and in obtaining the desired uniformity of thickness. Another way of attachment according to a description by the Bergquist Company of Minneapolis, Minn., is to use a tape that consists of a high performance acrylic, pressure sensitive adhesive, on both sides of a Kapton MT film. The tape has a clear release liner material on one face and a white release liner material on the other face. To install it, the clear liner is removed from one face and the tape is rolled onto the IC package substrate. Then the white liner on the other face is removed and the heat sink is pressed lightly (less than 10 pounds per square inch) onto the substrate. While the skill level required for this procedure may be less than that for a good application of the paste interface method, a problem can develop during the use of the electronic equipment of which the IC package is a part. This is due to the fact that some films of the Kapton type change from a solid to a fluid phase as they become warm. While this phase change enhances the thermal conductivity, without changing electrical resistivity, it can result in a problem of seeping of the material and resultant leakage in the electronic equipment, particularly if the plane of the interface is vertically oriented.